I do know that there’s a short form of the causative (From Wikipedia: A shortened causative form exists where the final -u becoming -asu for consonant stem verbs, and -ru becoming -sasu for vowel stem verbs), that would basically be the same thing.
動く’s normal causative is 動かせる, and the short form according to that rule would be, you guessed it, 動かす. So, in this case, maybe it just transitioned from being thought of as an intransitive in causative form, to just being thought of as a transitive verb in its own right.
I don’t know for sure though, that’s just piecing two things that make some sense to me together.
But in all honesty, StackExchange is the proper place to ask real questions about Japanese that might actually require knowledge or research. We don’t know jack here, comparatively.